F-82 Twin Mustangs

This unusual Rube Goldberg aircraft, which began as two P-51 Mustang fuselages, had a crew of two, and two Allison V-1710-143/145 engines, according to the 1951 Aviation Yearbook, which I must have bought when I was 11 years old [GPL].
According to David Hanson,

The P-82 came about as a result of a USAAF requirement for a very long range escort fighter for operations in the Pacific, especially to escort the B-29s all the way to Japan and back. The purpose of having two pilots was as a relief against fatigue on the long overwater missions. Only 20 of the 500 ordered had been built before the war's end brought a cancellation to the contracts, but 250 more were built in 1946. Part of this order was for a night fighter version (with a radar operator instead of a second pilot) which was made to replace the Northrop P-61 Black Widow. The P-82 was renamed the F-82 in 1948, and a U.S. F-82 shot down the first enemy aircraft of the Korean War. [source]